Dobsonflies, Fishflies, and Alderflies: Megaloptera

views updated




Adult alderflies measure 0.4 to 0.6 inches (10 to15 millimeters) in length, while dobsonflies and fishflies are 0.6 to 2.4 inches (40 to 75 millimeters). They are soft-bodied insects and are black, brown, or yellowish orange to dark green. The head is broad and flat and has chewing mouthparts that are directed forward. The antennae (an-TEH-nee), or sense organs, are long, feathery (fishflies), threadlike (dobsonflies), or beadlike (alderflies). Their compound eyes, or eyes with multiple lenses, are large. Only the dobsonflies and fishflies have simple eyes, or eyes with only one lens. The four wings of alderflies are held like a roof over the body when at rest, but those of dobsonflies and fishflies are kept flat. Megalopteran wings are membrane-like and have a complex network of veins that is not branched at the edges of the wings. The hind wings are broader than the forewings and are folded fanlike underneath them. The abdomen is ten-segmented and does not have any projections at the tip.

The larvae (LAR-vee), or young of animals, do not resemble the adults. Larvae of alderflies reach a maximum length of 1 inch (25 millimeters), while those of dobsonflies (known as hellgrammites) and fishflies measure 1.2 to 2.9 inches (30 to 65 millimeters). Their bodies are long and flat. The head is flat and has short antennae. The chewing mouthparts are directed forward. A hard, shieldlike plate covers each of the three segments of the thorax, or midsection. The first segment of the thorax is almost square in shape. The abdomen has seven or eight long slender abdominal gills on each side. The gills absorb oxygen from the water, allowing the larvae to breathe. In alderflies, the abdomen ends in a single, threadlike projection, but in dobsonflies and fishflies it ends in a pair of leglike structures, each with two hooklike claws.


Megalopterans live in North, Central, and South America, South Africa, Madagascar, and parts of Asia and Australia. Most species are found outside of the tropics. There are about 300 species of megalopterans worldwide, 43 of which are found in the United States and Canada.


Aquatic larvae live in standing or flowing waters, including streams, spring seeps, rivers, lakes, ponds, and swamps. Some species burrow in soft mud or sand, while others hide in crevices or under stones or bark. Adults are found on vegetation beside aquatic habitats.


The larvae actively hunt a wide variety of small aquatic insect larvae, crustaceans, clams, and worms. Adult alderflies may feed on flowers, while female dobsonflies and some fishflies take in plant sap or other fluids. Male dobsonflies do not eat.


The adults are short-lived and are seldom seen in large numbers. Alderflies are active during the warmest parts of the day and sometimes fly for very short distances. Most dobsonflies and fishflies are active at night and are attracted to lights. Their flight is slow and awkward, but they are capable of covering long distances.

Some alderflies and dobsonflies locate their mates with pheromones (FEH-re-moans), or special chemicals that attract males as mates. Male dobsonflies have very long jaws, which they use to battle other males over females. Males place their jaws over the wings of the female for a short time before mating. Megalopterans usually mate on plants near the water.

The life cycle of megalopterans includes four very distinct stages: egg, larva, pupa, and adult. Females attach layered masses of two hundred to three thousand eggs on objects that hang over the water. They usually select mostly shady sites that are protected from direct sun during the hottest time of day. The larvae drop into the water after hatching. They will molt, or shed their exoskeletons or hard outer coverings, ten to twelve times over a one- to five-year period before reaching the pupal stage. Mature larvae leave the water and pupate in a chamber dug in the soil or leaf litter near the shore. Adults usually emerge in late spring to midsummer and live for only a week or two.

The legs, wings, antennae, and mouthparts of all megalopteran pupae are distinct. These appendages are not attached along their entire length to the body. The pupae are also not enclosed in a cocoon.


The larvae of some species are important trout food and are used as fish bait. In the Japanese tradition, the dried larvae of some dobsonflies are thought to be a cure for children's emotional problems.


In spite of their fearsome appearance, male dobsonflies cannot deliver much of a bite. They simply do not have the muscle power necessary to generate enough force to drive the sharp tips of their long jaws into human flesh. However, when carelessly handled, the females are quite capable of using their short, sharp jaws to deliver a very painful bite.


No megalopterans are listed as endangered or threatened, but like all species that live only in small geographic areas, their populations are vulnerable to logging, pollution, and other human activities, as well as to natural events that lower water quality.


Physical characteristics: Adults measure up to 2 inches (50 millimeters) in length, with wingspans up to 5.5 inches (140 millimeters). The larvae, known as hellgrammites, are 2.6 inches (65 millimeters) long. The head is almost circular, and the first section of the thorax is slightly narrower than the head. The wings are see-through gray with dark veins and white spots. The jaws of the male are half as long as the body. They are curved and pointed at the tips and held crossing each other. The jaws of the female are shorter.

Geographic range: Eastern dobsonflies live east of the Rocky Mountains in the United States and Canada.

Habitat: The hellgrammites live in fast-flowing streams. The adults are found resting on streamside vegetation.

Diet: The hellgrammites eat small insect larvae, crustaceans, clams, and worms. Adult females drink various fluids, but the males do not drink or eat.

Behavior and reproduction: Adults are active at night during the summer and are sometimes attracted to lights. They are seldom seen during the day, spending most of their time hidden under leaves high up in trees. The larvae usually crawl on the bottom of the stream. Sometimes they move like a snake, swimming forward and backward in the water.

Males use their big jaws as weapons against other males over females. Courtship behavior is limited but does include fluttering of the wings. Females lay one hundred to one thousand eggs in round masses on rocks, branches, and other objects close to the water. Each mass is coated with a chalky, whitish substance. The larvae drop into the water or crawl to the nearby stream. They take two to three years to reach the pupal stage. Mature larvae crawl out of the water to dig their pupal chambers beneath logs and rocks along the shore.

Eastern dobsonflies and people: Fishermen use hellgrammites as bait for trout, largemouth bass, catfish, and other fishes. Eastern dobsonflies also help control populations of aquatic pest insects such as the Asian tiger mosquito.

Conservation status: This species is not listed as endangered or threatened. ∎



Evans, E. D., and H. H. Neunzig. "Megaloptera and Aquatic Neuroptera." In An Introduction to Aquatic Insects of North America, edited by R. W. Merritt and K. W. Cummins. 3rd edition. Dubuque, IA: Kendall/Hunt Publishing Company, 1996.

McCafferty, W. P. Aquatic Entomology: The Fisherman's and Ecologist's Illustrated Guide to Insects and Their Relatives. Boston: Jones and Bartless Publishers, 1981.

Tavolacci, J., ed. Insects and Spiders of the World. Volume 1: Africanized Bee-Bee Fly. Volume 3: Carrion Beetle-Earwig. New York: Marshall Cavendish, 2003.

Web sites:

"Dobsonflies." Critter case files. (accessed on October 17, 2004).

Eastern dobsonfly. (accessed on October 17, 2004).

Megaloptera. Alderflies, dobsonflies. (accessed on October 17, 2004).

"Megaloptera. Alderflies, dobsonflies, fishflies." Tree of Life. (accessed on October 17, 2004).

About this article

Dobsonflies, Fishflies, and Alderflies: Megaloptera

Updated About content Print Article